Amnion invasion assay was used to quantitate migration of inflammatory and tumor cells through human connective tissue barriers. Polymorphonuclear leucocyte migration through the amnion was demonstrated by optical and electron microscopy. The rate of polymorphonuclear migration was stimulated by the chemoattracatant N-formylmethionyl-leucyl phenylalanine (FMLP). Adherence studies of polymorphs to components of the basement membrane show that they use laminin to attach to type IV collagen. M5076 cells which secrete proteases to all the known types of collagen traverse the amnion within 24 hours. In the presence of the chemoattractant, FMLP, the rate of invasion is significantly increased. On the contrary, inhibition of invasion is seen with bovine cartilage extract and purified metalloproteinase inhibitor. Treatment, with crude and purified interferon of Ewing sarcoma cells increase their invasive capacity through the amnion basement membrane. Human or bovine endothelial cells grow to confluency on amnion basement membrane (BM). Tumor cell invasion is significantly retarded by the endothelial cell monolayer. Adult rat hepatocytes attach better to the amnion BM than to any of the five types of collagen tested and can be kept alive in a defined medium for three weeks.